FIELD OF THE INVENTION
The invention relates to novel bis-o-aminophenols and bis-o-aminothiophenols, which are also jointly abbreviated to bis-o-amino(thio)phenols, and to a process for their preparation.
Bis-o-aminophenols are needed, in particular, for the preparation of high-temperature-stable polymers, such as polybenzoxazoles (PBOs) and their precursors and for the preparation of hydroxypolyimides (in this respect, see, for example, EP 0 264 678 B1 and EP 0 300 326 B1). PBO precursors can be prepared by reacting a dicarboxylic acid chloride with a bis-o-aminophenol. However, whereas numerous dicarboxylic acids and chlorides thereof are available owing to the wide variety of potential industrial applications, there are comparatively few bis-o-aminophenols. In addition the nature of the aminophenol used has a strong effect on the property profile of the polymer prepared therewith. For example, not only the thermal, electrical and mechanical behavior, but also the solubility and hydrolysis stability and numerous other properties of the polymer are greatly affected by the aminophenol used in the preparation. PBO precursors in the form of a photosensitive composition can be structured inexpensively by direct methods, i.e. without an auxiliary resist. Compared with other dielectrics which can be photostructured directly, such as polyimide (PI) and benzocyclobutene (BCB), PBO precursors offer the advantage of positive structurability and aqueous-alkaline development (see EP 0 023 662 B1 and EP 0 264 678 B1). To this end, the PBO precursors used must be substantially transparent at the exposure wavelength and sufficiently soluble in the developer, which preferably contains no metal ions. Like polyimides, polybenzoxazoles also have the major advantage that, compared with the cyclized final product, they can be applied to a substrate as readily soluble precursors and then cyclized, during which the solubility and thus the sensitivity to solvents and other process chemicals decreases greatly.
In addition to good electrical, mechanical and thermal properties, use of polybenzoxazoles in microelectronics, in particular as dielectric between two metal planes, for example in multi-chip modules and memory and logic chips, or as buffer coat between the chip and its housing, also requires low moisture absorption; this is because the moisture content in the polymer layer impairs the electrical properties of the polymer and also can result in bubble formation and flaking at high temperatures. A good planarization capacity of the polybenzoxazoles is likewise advantageous since production of components using a dielectric which produces good planarization allows expensive polishing procedures (chemical mechanical polishing, CMP) to be avoided.
Aminophenols which are suitable for the preparation of readily soluble PBO precursors are disclosed, for example, in U.S. Pat. No. 4,525,539 and EP 0 317 942 A2. However, there is no indication therein of the moisture absorption or planarization behavior of the resultant polymers after cyclization on the substrate (see EP 0 264 678 B1 and EP 0 317 942 A2). In the preparation of the aminophenols, a phenolic starting compound is nitrated. If the nitration does not take place completely, i.e. to 100%, and entirely free from isomers, i.e. nitration may only take place in the o-position to the hydroxyl group, reduction of the nitro group in some cases results in aminophenols, which do not allow complete cyclization in the PBO precursor and considerably impair the properties of the polybenzoxazole. This is a major disadvantage of the known preparation processes.
SU 1 205 518 A discloses aromatic aminophenols. However, polybenzoxazoles prepared from these aminophenols are not stable at high temperatures, showing 1% weight loss already at 420-430.degree. C. The preparation of these aminophenols also uses carcinogenic hydrazine hydrate, which is a considerable disadvantage. In addition, there is again no indication of the moisture absorption and planarization behavior of the resultant polymers after cyclization on the substrate.
A process for the preparation of bisaminophenols is also disclosed in "Polymer Preprints" 34 (1), 1993, pages 425 and 426. This process has the disadvantage of requiring high temperatures, i.e. significantly higher temperatures than 100.degree. C. (solutions in dimethylacetamide and toluene are refluxed). However, high reaction temperatures promote side reactions, which reduce the yield (which is a maximum of 73%) and make purification of the target product more difficult. There is likewise no indication herein of the moisture absorption or planarization behavior of the resultant polymers after cyclization on the substrate.